This invention relates to emergency evacuation equipment for aircraft, in particular to an inflation device for inflating an inflatable aircraft evacuation slide or other inflatable device. The requirement for reliably evacuating airline passengers in the event of an emergency is well known. Emergencies at take-off and landing often demand swift removal of passengers from the aircraft because of the potential for injuries from fire, explosion, or sinking in water. A conventional method of quickly evacuating a large number of passengers from an aircraft is to provide multiple emergency exits, each of which is equipped with an inflatable evacuation slide. Current state of the art emergency evacuation slide systems comprise an inflatable evacuation slide that is stored in a folded, uninflated state together with a source of inflation gas. The source of inflation gas typically comprises a gas generator, stored compressed gas, or a combination thereof. Pyrotechnic gas generators have an advantage in that they are small, lightweight, and produce a high volume of gas, however, the high temperature gas produced by a gas generator alone can cause numerous problems including sagging of the evacuation slide as the inflation gas cools and, in some cases melting or scorching of the fabric out of which the inflation slide is fabricated.
Use of stored compressed gas by itself, although simple, implicates a weight penalty that must be paid for carrying a pressure vessel having sufficient capacity (in terms of volume and pressure) to inflate the evacuation slide over the wide operational temperature range specified for such slides. Additionally, where only a compressed gas is used to inflate the evacuation slide, a large drop in temperature occurs as the gases expand, often causing ice to form, which can block the flow of gas. Accordingly, state of the art emergency evacuation slide systems typically comprise a hybrid inflator, which utilizes a stored compressed gas together with a pyrotechnic gas generator. The pyrotechnic gas generator augments the stored compressed gas by providing additional gas as well as heat to counteract effects of the expansion-induced cooling of the compressed gas as it expands out of the pressure vessel.
To further augment the volume of gas delivered to the evacuation slide, many evacuation systems utilize aspirators such as that disclosed in U.S. Pat. No. 4,368,009 to Heimovics, et al. As the compressed gas flows through the aspirator, a venturi draws additional air into the aspirator to pump about two to three times as much gas into the evacuation slide as is supplied by the gas source alone.
Despite these advances, there still exists problems due to the wide ambient temperature range over which these inflation systems are required to operate, typically from −65° F. to +160° F. The amount of gas available must be enough to pressurize the evacuation slide at the coldest temperature. Because of the relationship between pressure and temperature within a fixed volume, however, as the ambient temperature rises above the minimum, the pressure within the pressure vessel rises proportionately. Accordingly, at higher temperatures, the inflation system produces substantially more gas than is necessary to inflate the evacuation slide. To prevent overpressurization and possible rupturing of the inflatable evacuation slide, provisions must be made to vent the excess inflation gas.
A conventional method of venting the excess inflation gas is to provide several pressure relief valves in the inflatable slide itself. Pressure relief valves, however, add significant weight to the inflatable evacuation slide and add substantial volume to the inflatable slide in its uninflated, stored condition. According to U.S. Pat. No. 6,240,951 to Yori and assigned to the assignee of the present invention, excess inflation gas may be vented by means of a regulator valve that includes an active waste gate, which vents excess gas as the pressure in the outlet port of the regulator valve rises. Although the valve of Yori accomplishes the function of venting excess inflation gas it does so at the cost of substantial complexity and cost.
Accordingly, what is needed is a simple and inexpensive control valve for an aircraft emergency evacuation slide that reliably vents excess inflation gas thereby eliminating or reducing the number of pressure relief valves required in the slide itself.